Cystic Fibrosis (CF) is the number one genetic cause of death in the Caucasian population, affecting 1 in 2000 births, and is an obvious candidate disease for gene therapy. Recent studies in our laboratory evaluating the cellular sites which express CFTR in the lung have identified multiple potential cellular targets in the conducting airways and bronchial submucosal glands. The lack of an effective means to target submucosal gland region in gene therapy is predominantly due to a lack of understanding about the cellular mechanisms of gland development and progenitor cell targets. To this end we have developed two animal models including the ferret and human bronchial xenograft which have been useful in identifying the progenitor cells of submucosal glands in the adult and fetal airway epithelium. By using recombinant viral technology, we will investigate two approaches to identify submucosal gland progenitor cells in the airway which give rise to CFTR expressing submucosal glands and the mechanisms by which epithelial-mesenchymal interactions may affect these processes. These approaches include 1) the use of retroviral and AAV reporter genes to track the fate of surface airway epithelial cell types during reconstitution of the various cellular components of submucosal gland, and 2) the use of recombinant retroviral gene transfer to study the effect of mesenchymally expressed ctyokines in these processes. These approaches, in combination with models of gland developing airways in which specific mesenchymal and epithelial cellular components can be reconstituted and genetically manipulated, will allow for dissection of the components in the airways which are important in gland development. Additionally, the localization of mesenchyme expressed cytokines and epithelial expressed cytokine receptors will also lend insight into the mechanisms by which cellular fates are determined in gland formation. Elucidation of the target cells and mechanisms involved in submucosal gland formation may lead to the development of methods for gene therapy in the adult human airway by targeting submucosal gland progenitor cells involved in de novo gland formation from the surface airway epithelium is well as by targeting submucosal gland stem cells in utero. The rational approach to gene therapy of the submucosal gland regions of the lunge will also require knowledge of the pathophyiologic importance of these region in CF. Utilizing models of the airways with and without submucosal glands, we will also attempt to evaluate the contribution of submucosal glands in several functional endpoints which have been proposed to be important in the progression of CF lung disease including electrolyte and fluid transport. By defining the contribution submucosal glands have on these processes, we hope to address the potential pathophysiologic importance of these regions as targets for gene therapy in CF lung disease.